(1)设直线的截距式为x/a+y/b=1.(a>0,b>0)
直线过点(1,2),所以1/a+2/b=1.
1=1/a+2/b≥2√(2/(ab)),
平方:1≥8/(ab),ab≥8
面积S=1/2ab≥4.(a=2,b=4时取到等号)
(2)因为1/a+2/b=1
所以a+b=(a+b)( 1/a+2/b)
=3+b/a+2a/b≥3+2√2.(b/a=2a/b时取到等号)
(1)设直线的截距式为x/a+y/b=1.(a>0,b>0)
直线过点(1,2),所以1/a+2/b=1.
1=1/a+2/b≥2√(2/(ab)),
平方:1≥8/(ab),ab≥8
面积S=1/2ab≥4.(a=2,b=4时取到等号)
(2)因为1/a+2/b=1
所以a+b=(a+b)( 1/a+2/b)
=3+b/a+2a/b≥3+2√2.(b/a=2a/b时取到等号)